Human lung organoids develop into adult airway-like structures directed by physico-chemical biomaterial properties

Abstract

Tissues derived from human pluripotent stem cells (hPSCs) often represent early stages of fetal development, but mature at the molecular and structural level when transplanted into immunocompromised mice. hPSC-derived lung organoids (HLOs) transplantation has been further enhanced with biomaterial scaffolds, where HLOs had improved tissue structure and cellular differentiation. Here, our goal was to define the physico-chemical biomaterial properties that maximally enhanced transplant efficiency, including features such as the polymer type, degradation, and pore interconnectivity of the scaffolds. We found that transplantation of HLOs on microporous scaffolds formed from poly (ethylene glycol) (PEG) hydrogel scaffolds inhibit growth and maturation, and the transplanted HLOs possessed mostly immature lung progenitors. On the other hand, HLOs transplanted on poly (lactide-co-glycolide) (PLG) scaffolds or polycaprolactone (PCL) led to tube-like structures that resembled both the structure and cellular diversity of an adult airway. Our data suggests that scaffold pore interconnectivity and polymer degradation contributed to the maturation, and we found that the size of the airway structures and the total size of the transplanted tissue was influenced by the material degradation rate. Collectively, these biomaterial platforms provide a set of tools to promote maturation of the tissues and to control the size and structure of the organoids.

Introduction

Human lung organoid models facilitate the study of cell fate decisions during development and for modeling diseases such as cystic fibrosis and goblet cell metaplasia, and infections such as respiratory syncytial virus [[1], [2], [3], [4], [5], [6], [7], [8]]. We have previously demonstrated that human pluripotent stem cell (hPSC)-derived human lung organoids (HLOs) possess a complex tissue structure in vitro, which includes both the epithelium and supporting tissue (cartilage, smooth muscle, fibroblasts) [1,9].

Notably, in vitro HLO cultures reflect the fetal airway, with adult airway-like structures generated only after in vivo transplantation [9]. Maturation following in vivo transplantation of HLOs reflects observations with numerous other organoid and hPSC-based systems [1,[10], [11], [12], [13]],. While many other studies have shown successful transplantation of hPSC-derived tissues under the kidney capsule or other vascular sites within the murine host, HLOs required the assistance of a PLG microporous polymer scaffold to support engraftment and vascularization following transplant into the epididymal fat pad of immunocompromised mice. After 8 weeks, the transplanted HLO (tHLO) had airway-like structures that resembled native adult airways including proper cellular organization, epithelial cellular ratios and airway cell types. Airway-like structures were also surrounded by smooth muscle and possessed cartilage, as would be the case in the human airways [9]. However, these previous studies did not identify the polymer scaffolds design parameters that conferred an engraftment and growth advantage for HLOs.

In this report, we investigated the physico-chemical properties of microporous scaffolds that support HLO maturation into airway structures. Polymers have different degradation rates and may have distinct interactions with the host, so microporous scaffold support of transplanted HLO were tested using diverse materials including poly (lactide-co-glycolide) (PLG), polycaprolactone (PCL), and poly (ethylene glycol) (PEG). The interconnected pore size was varied, as well, through the initial scaffold fabrication and also through the degradation rate of the polymers. For these material platforms, we investigated airway maturation, immune response, as well as overall explant and airway size. Identifying the biomaterial design parameters that influence airway maturation and structure will enable the development of platforms that can direct the structure to better model airway homeostasis and disease environments.